We want test caching to work even for people with scripts
that set a non-default test timeout. But then that raises the
question of what to do about runs with different timeouts:
is a cached success with one timeout available for use when
asked to run the test with a different timeout?

This CL answers that question by saying that the timeout applies
to the overall execution of either running the test or displaying
the cached result, and displaying a cached result takes no time.
So it's always OK to record a cached result, regardless of timeout,
and it's always OK to display a cached result, again regardless of timeout.

Fixes #22633.

Change-Id: Iaef3602710e3be107602267bbc6dba9a2250796c
Reviewed-on: https://go-review.googlesource.com/76552
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: roger peppe <rogpeppe@gmail.com>
Reviewed-by: David Crawshaw <crawshaw@golang.org>